A social network is a structure that represents people and relationships between those people. A social network for a given person may be thought of as that person, and those people to whom that person is connected via relationships. Two people may be directly connected where there is a relationship between those people (e.g., they know each other), and this may be thought of as those people having one degree of separation. Similarly, two people may be indirectly connected where they do not have a direct relationship, but do have a direct relationship with a common person (e.g., they both know the same person), and this may be thought of as those people having two degrees of separation. It may be appreciated that people may be even more tenuously connected in indirect relationships—e.g., three degrees of separation or more.
A social networking service, then, is a computer system that implements a social network across a computer network. For instance, people may log in to a social network service from their mobile device to access data stored on a social networking server—such as data that represents the social network connections that people have with each other. A person who uses a social networking service may add or delete connections or friends on that service, and communicate with those connections or friends by way of that service.